臭氧-活性碳生物濾床對於消毒副產物生成潛勢之影響 : 以金門太湖淨水廠為例

Disinfection Byproduct Formation Potential Reduction by Ozonation-Biologically Active Carbon Filtration: A case study on Kinmen Island

吳聖培(Sheng-Pei Wu)

指導教授 ： 童心欣

國立臺灣大學/工學院/環境工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.02187

摘要

金門太湖原水在營養鹽較高的情況下，往往有優養化以及季節性藻華的影響，使得水中含有大量的溶解性有機物。在經過自來水水廠一系列的處理程序，於加氯消毒會生成大量的消毒副產物，如：三鹵甲烷、鹵乙酸等。相較有濃度管制的碳系消毒副產物，許多有較高毒性的氮系消毒副產物如：鹵化硝基甲烷、鹵乙腈、鹵化乙醯銨等，近期也受到相當的重視。將臭氧作為氧化劑進行前氧化處理時，疏水性有機物轉化為親水性有機物，增加生物可降解性有機碳的比例。以利在後續活性碳生物濾床降低溶解性有機碳濃度，進而降低消毒副產物的生成濃度。本研究欲利用臭氧-活性碳生物濾床對水質進行改善，目的在於降低溶解性有機碳濃度，進而降低在加氯過程中生成之消毒副產物。利用批次多循環式臭氧-活性碳生物濾床程序，在相異消毒劑與不同循環次數下，對溶解性有機碳以及消毒副產物生成潛勢去除進行評估。同時在後續使用連續流的方式進行操作，並且加入醋酸鈉作為刺激物以利微生物在濾床中生長，評估溶解性有機碳與前質是否有加強去除。實驗結果顯示，在1至3次多循環式臭氧-活性碳生物濾床後，相較於太湖淨水廠之原水，可分別降低48%、53.2%、75.9% 之溶解性有機碳濃度，另外，在經過第三次的循環處理後，以次氯酸納為消毒劑時，可降低90.7% 之總三鹵甲烷生成潛勢以及86.7% 之鹵乙酸生成潛勢，若以氯胺為消毒劑時，可降低81.3% 之總三鹵甲烷生成潛勢以及87.6% 之鹵乙酸生成潛勢。在鹵乙酸的生成上，臭氧在減少三鹵乙酸生成潛勢的同時會增加二鹵乙酸生成潛勢，但在活性碳生物濾床過濾後皆會減少。在鹵乙腈生成上，在臭氧曝氣後的生成動力上發現臭氧可以去除大部份的鹵乙腈前質，但經過後續的臭氧程序後，依然有部份鹵乙晴的前質未被去除，而在生成潛勢上，在過濾程序中可以有效地降低。同時，在相同的加藥劑量下，若是以次氯酸鈉做為消毒劑時，相較於氯胺，在反應初期所生成的濃度較高。臭氧加強了三氯硝基甲烷的生成，但在後續的活性碳生物濾床降低了三氯硝基甲烷的濃度。在連續流的操作上，加入次氯酸鈉作為刺激物在有機物的去除上僅有些微的幫助，對於去除三鹵甲烷、鹵乙酸、鹵乙腈以及三氯硝基甲烷的前質上沒有太大影響。於此，利用臭氧-活性碳生物濾床可以改變有機物的性質，降低溶解性有機碳與總三鹵甲烷以及鹵乙酸之生成潛勢。而在後續的消毒程序上，氯胺不僅在總三鹵甲烷以及鹵乙酸的生成量上較低，同時在反應前期所生成的鹵乙腈亦較少，這些結果支持以臭氧-活性碳生物濾床做為處理程序的同時，在後續以氯胺做為消毒劑的情況下，可以在反應前期生成較少的碳系以及氮系之消毒副產物濃度，降低在用戶端上所造成的暴露風險。

關鍵字

臭氧 ； 生物活性碳 ； 鹵乙腈 ； 消毒副產物生成潛勢

並列摘要

Tai Lake, one of the major water sources on Kinmen Island, suffers from eutrophication and seasonal algae bloom due to livestock farming and agricultural husbandry. The conventional treatment process can only remove partial dissolved organic carbon. Therefore, disinfection by-products (DBPs), such as trihalomethanes (THMs), haloacetic acids (HAAs), and halonitromethanes (HNMs), haloacetonitrile (HANs) were a major concern in finished water. Ozone, a strong oxidant, can remove hydrophobic organic compounds effectively. Combined with biologically active carbon (BAC) filtration, it can reduce dissolved organic material and reduce DBP formation in finished water. The objective of this study was to reduce dissolved organic carbon (DOC) and DBP formation by operating ozonation-BAC in multiple repeating cycles. DBP formation potential (DBPFP) and formation kinetics were used to evaluate DBP precursors removal efficiency with different disinfectants. In the continuous mode, sodium acetate solution was used as stimulant for biostimulation to evaluate if the removal efficiency of THM4, HAA9, HANs and trichloronitromethane were enhanced. After ozone-BAC, DOC removal efficiency with 1 to 3 times ozone-BAC process were 48%, 53.2% and 75.9%, respectively. THM4 and HAA9 formation potential were also reduced by multiple ozone-BAC processes. After 3 times ozone–BAC, the removal efficiency of THM4 and HAA9 formation potential was 90.7%, 86.7% with sodium hypochlorite, and 81.3%, 87.6% with monochloramine, respectively. For the haloacetics acids, ozonation could reduce the formation potential of trihaloacetic acids but enhance the dihaloacetics acids formation potential. At the same time, dihaloacetics acids and trihaloacetic acids formation potential could be reduced after BAC filtration. As for nitrogenous-DBPs, ozonation could remove most precursors of the HANs. The overlapping of formation kinetics indicated that some of HANs precursors still remained after ozonation. In addition, HANs formation potential was reduced during BAC filtration process. With the same dosage, concentration of HANs was higher with sodium hypochlorite than with mono-chloramine in the beginning of the reaction. Ozonation enhanced the formation concentration of trichloronitromethane; meanwhile, it was reduced after BAC filtration. In the continuous mode, the addition of sodium acetate could slightly improve the removal of DOC. However, the removal of precursors of trihalomethanes, haloacetic acids, haloacetonitriles and trichloronitromethane was remained the same. In summary, ozonation and BAC filtration can reduce dissolved organic carbon concentrations as well as THM4 and HAA9 formation potential successfully. In the subsequent disinfection, mono-chloramine not only produces lesser THM4 and HAA9 but also reduces the HAN formation. These results provide evidence that the ozonation-BAC-monochloramine process can reduce the DBP concentration successfully in high organic water.

並列關鍵字

Ozone ； biologically activated carbon (BAC) ； haloacetonitrile ； disinfection by-products formation potential (DBPFP)

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